Solid oxide fuel cells (SOFCs) including a solid oxide as a solid electrolyte are one kind of fuel cells.
Solid oxide fuel cells including lanthanum strontium cobaltite ferrite (LSCF) as an air electrode are also known (for example, JP 2001-196083A (PTL 1). There is a report that LSCF in the air electrode is poisoned by S (sulfur) in SOx contained in air in contact with the air electrode, particularly SO2 (Wang et al., J. Electrochem. Soc., 158, B1391 (2011) (NPL 1)). This literature reports that, in solid oxide fuel cells including an air electrode made of LSCF as an air electrode, sulfur is reacted with Sr (strontium) in LSCF to form SrSO4 on the surface of LSCF, disadvantageously leading to lowered power generation performance. As far as the present inventors know, there is no report that approvingly interprets the presence of sulfur in the air electrode before the use of the solid oxide fuel cell.